Pendulum-type torsional damping devices, also called pendulum oscillators or pendulums, which in particular but not exclusively are part of the transmission of a motor vehicle, are known from the existing art.
In a motor vehicle transmission at least one torsional damping device is generally associated with a clutch capable of selectively connecting the engine to the gearbox, such as a friction clutch or a hydrokinetic coupling device having a lockup clutch, the purpose being to filter vibrations due to engine irregularities.
This is because a combustion engine exhibits irregularities due to the successive combustion events in the engine cylinder, said irregularities varying in particular as a function of the number of cylinders.
The damping means of a torsional vibration damper consequently have the task of filtering vibrations caused by the irregularities, and they act before driving torque is transmitted to the gearbox.
Otherwise the vibrations penetrate into the gearbox, where they would cause particularly undesirable impacts, noise, or acoustic annoyances during operation.
This is one of the reasons for using one or more damping means capable of filtering vibrations at at least one defined frequency.
The document U.S. 2010/122605 describes a damping device of the pendulum type.
The damping device comprises at least one support rotationally coupled to an engine shaft and at least one oscillating mass, generally several oscillating masses circumferentially distributed on the support. The oscillations of these oscillating masses generate an oscillating torque that acts against the oscillating torque coming from the engine and thus absorbs a portion of the engine's irregularities. The support, sometimes called a “phase washer,” of the torsional damping device is typically integral with the driving shaft.
Each oscillating mass is generally constituted by a pair of flyweights arranged on either side of the support and integral with one another either by way of a direct mechanical connection, typically through an opening of the support, or by means of a spacer. An assemblage of this kind of two flyweights integrated face to face, with or without a spacer, is regarded hereinafter as a single oscillating mass.
Alternatively, each oscillating mass can be a single flyweight mounted movably on the support. In this case the support can optionally be constituted by two elements, the oscillating masses being arranged movably between those two elements.
An oscillating mass of this kind is very generally mounted movably on the support by means of at least one bearing element, typically via two bearing elements or even more.
Typically the center of mass of each oscillating mass is free to oscillate around an oscillation axis substantially parallel to the rotation axis of the engine shaft and driven rotationally around that rotation axis.
The oscillating masses move in reaction to the rotational inconsistencies in such a way that the center of mass of each of them oscillates around that oscillation axis.
The radial position of the center of mass of each of the oscillating masses with respect to the rotation axis of the driving shaft, as well as the distance of that center of gravity with respect to the oscillation axis, are established so that in response to centrifugal forces, the oscillation frequency of each of the oscillating masses is proportional to the rotation speed of the driving shaft, that multiple being capable of assuming, for example, a value close to the preponderant harmonic order of the irregularities.
The desire for increasingly effective vibration filtering is leading to refinements of pendulum-type torsional damping devices.
It was found in particular that the use of a pendulum comprising two bearing elements (or rollers) for each oscillating mass, called a “bifilar pendulum,” yielded better damping performance than a pendulum comprising only one bearing element for each oscillating mass, called a “monofilar pendulum.”
The existing art thus leads to a choice between using a bifilar pendulum that performs well but is of complex design, and a monofilar pendulum that has a relatively simple design but relatively modest performance.